Telephone system



fr.' F. cRocKER TLPHONE SYSTEM J'ily AFiled March 2:5, 192 El 5 Sheesheet 1 Imns'zm7V vT11/.7111515 F. EFC/cker July 1o, 192s.l

l T. F. CROCKER TELEPHONE SYSTEM :s sheets-sheet 2 Filed March 23, 1925 -lmrez'z 01"- hamas F. Cracker July 10, 1928.

T. F. CROCKER TELEPHONE SYSTEM s sheets-sheet '3 Filed March 25, 1925 -I-Imrerz DP- Thnmas Cracker Patented Jui] 1Q, if.

in.tiras stares tartar z ric.

THOMAS r. erweisen, or CHICAGO, rrr-titers, assienoarnv Mnsnnfassrenivinivrs, 'ro

AUTOMATIC nrncraic rive., or cnrcaeo, trainers, A CORPORATION OFDELA- -WARE Application inea March 23, 1925. serial N.'17,53`9.

rthis invention relates to telephone systems in general, but is lmore particularly con ce1-ned with automatic telephone systemsof relatively small size, commonly vknown as private automatic exchanges.

A private automatic exchange is usually employedto serve special groups of subscribers, such as in a factory or business organization. Better service is obtained between substations within'the organization if the service is given by a private exchange, which obviates the necessity of calling through a central office. automatic exchangahowever, may have access to the central ottico by means of trunks or groups of trunks, and may also give service to individual 'common battery telephone substations reserved for officials who desire special service. f

in such a system it may be required to give restricted service to some substations and unrestricted service to other substations; and it is the principal robject of this iiiveiition to provide simple and eflicient trunk circuits and a. new universal cord circuit for the attendants switchboard for completing the several types vof calls and rendering the different kinds of service required.

A special feature of this invent-ion relates to improved circuits which ai'e so arranged as to prevent the attendant from setting up an unauthorized connection between two socalled restricted substations, should she atempt to do so in the ordinary way, by in- Y advertence or mistake. Y

A further feature is concerned with means in the attendants cord circuit which ina-kes it impossible for the attendant to complete an unauthorized connection, either electrr caliy or n'ieclianically, by a combination of cords or keys, should she attempt to do so deliberately, with the object of defrauding the conipany.

These features of the invention, and others, will be fully described in connection withthe explanation of the various operations perforiiied in the private automatic exchange described below, reference being had to the accompanying drawings.

rlie telephonev system illust-rated for the purpose of describing this invention consists of a private automatic exchange, one or more associated common battery manual switchboards which are connected with tn e Such a private Y classes, one class having restricted service.

and the oth-er class having unrestricted service. The restricted substations have access to any other private automatic substation and may obtain connection by the attendantthrough herV cord circuit to any of the special common battery substations or to the common battery manual switchboards in the system, but are denied service to the outside main automatic exchange. The substations in the unrestricted class may vobtain connection with any substation in the system and also with the main automatic exchange. The common battery substations ory the common battery manual boards are not restricted and may obtain connection with any .of vthe private automaticv substations or with the 'main'automatic exchange throughth-e attendants cord circuit." yCalls from the cenf trai automatic exchange, however, are denied connection to the private automatic'substa-tions in the restricted class, but may obtain connection with the unrestricted private automatic substations and also with the common battery substations andV common battery manual switchboards. Y

Referring now to the drawings, tl e three figures placed end to end in numerical order show enough of the essential elements'of the specific telephone system thus briefly described to illustrate and explain the inven.- tioin In Fig. l are represented two of the private automatic substations, the vautomatic switches, and the trunk circuits that are brought into operation when a Subscriber at a private automatic substation calls the attendant, or the attendant completes a call to a private automatic substation. Fig. 2 is a diagram of the new universal cord circuit at the attendants position. In Fig. 3 are represented a trunk to a central automatic exchange, a line to a common battery telephone, and a trunk to a common battery manual switchboard, with their respective associated trunk and-line circuits.

vUl

'loo

Y service.

'The apparatus shown in the drawings will new be explained more in detail. The substations A and A in Fig. l are ordinary automatic telephones havinglines consisting of conductors 2 and 3, and 4 and 5, respectively. Substation A is given restricted service while substation A is allowed unrestricted service. Associated with each telephone line at the automatic exchange is an individual line switch, such as the line switches'LS or LS which are individual'to substations A and A', respectively, Fig. 1. The line switches are ot' the common rotary type in which they wipers have no normal position and move ina forward direction only. The total number otline switches is divided into groups, each group having aci cess to a group ot selectors. Vlhen a call is initiatedat a. substation,r the line switch of selector in the associated O'rou `of selectors.

.es p

The selectors, one of which is indicated byv reference letter S, Fig. l, are ot' the usual Strowger vertical and' rotary type, having bank contacts arranged in horizontal rows or levels. y y

.The selectorshave access to groups ot trunks terminating at the attendants cabinet and also to groups ot connectors.V ln this `particular case it will beassumed that the tenth orfzero levelris assigned to the v group of trunks reserved Vtor service to the main automat-ic exchange and is accessible only to tho-se substations which. have unrestricted It is further assumed that the ninth level is'assigned to the group of vtrunks reserved tor information service and 'for calls tothe common battery manual switchboard and common battery substations. This group vof trunks is accessible to all substations, restricted as wel.. as non-restricted. Means are provided in the selectors, and in the line switches associated with the substations sssigned to restricted service, for preventing the restricted substations trom obtaining' service or service to the common battery telephones orto the common battery manual switchboards.4 f

Each private automatic substation has a multiple jackv at the attendants cabinet, vwhichenables the attendant to complete incoming calls to the private automatic substaproper ninnber.

tions direct. rlhe jack J2 is the jack associated with the substationA, while jack J3 is the ack associated with the substation A.

The attendants switchboard or cabinet is provided with a plurality of cords, and an operators headset, the circuits of whichv are shown in Fig. 2, where they are indi# cated by reference characters CC and HS, respectively. The answering plug of the cord is labeled P and the calling plug is labeled P. The usualringing, listening, and dialling keys are provided. Means are provided in the operatorls head set and in the cord circuits which prevent the head set from being connected yto more than one cord at one time. Common to the cords is a flash and transmitter cutbil' key K2 for giving a flash-back signal to a manual operator ot the common battery switchboard or for short circuiting the transmitter.

The line from substation B, comprising conductors 217 and E218,v Fig. 3, terminatingv ,at the attendants cabinet in the jack J5, is

a line trom one oit the individual common battery substations. f y,

Several groups ot' two way trunks, each group assigned to a common battery manual switchboard associated with the private automatic system, terminate at .the attendants switchboard, each trunk endingV in a jack, such as J, with an associated trunk circuit T04. These trunks are accessible at the common battery manual operators position by way of jacks such as J7; Associated with each jack is a drop signal, suc-h as drop 311. Another group of two-way trunks is pro vided i'or the central automatic exchange, each trunk terminating at the private automatic attendants switchboard in a jack such as J4, with an associated'trunk circuit such as TG2., These trunks are accessible in the central automatic exchange via the banks ot connectors, as indicated, and terminate in individual line switches, such as L52, which are of the ordinary rotary type smilar to. LS and LS. l j

Having described the system and the ap paratus in general, a. more detaileddescription ot the operations performed in setting up calls between various su'bstations will be given. The assumption is first made'that a substation which has unrestricted service, such as A, desires connection with oBe of the individual commen battery substations, such asB. The subscriber at A, in order to make the call, lifts his receiver and Adials the i Since it has been assumed that the trunks to the attendant reserved for service to the common battery substations are accessible in the ninth l vel of the selector banks, the number to be dialled will be 9..

When the subscriber at sub-station A removes his receiver, a bridge is placed across the conductors t and 5, thereby completing a reaaso circuit v'for the line relay T of the line switch LS. The line relay 7 energizes and completes a circuit trom ground by way et armature 13 and its working ,cont-act, winding of switching relay 6, resting contact of armature 15 and said arma-ture, winding oli the stepping magnet 8 to battery. At armature 14, .the test wiper 19 connected to the junction ot the switching relay 6 and the stepping magnet 8.

1n case the trunk upon Awhich the wipers of the line switch are resting is idle', switch,- ing relay 6 energizes immediately. Assuming the trunk to be busy, however, switching relay 6 is short circuited trom ground on the test wiper: v19 and does Anot energize. lVipers 17-20, inclusive, are rotated step by step in a. buzzer-like manner by the a-ction of the stepping magnet 8, which operates from ground on the busy test Contacts encountered by the test wiper 19. When an idle trunk is reached, which will be assumed to be the trunk comprising conductors 21-24,

inclusive, stepping magnet 8 will ycease its stepping action. rEhe switching relay 6, being no longer short circuited, energizes in series with the stepping magnet 8.v lThe stepping magnet 8 does not operate at this time on account of the high resistance of the switching relay 6. The operation of the. switching relay 6 opens the test circuit and prepares the holdin0- circuit lor itself at armature 11. z: and at armatures 9 and 12 disconnects the line conductors 4 and 5 from the windin' of the line relay 7 and ground, 'and extends them by way of wipers 17-and 20, contacts 96 and 99, conductors 21 and 24, armatures 39 and 42 and their bank contacts, to the upper and lower windings oli' line relay 25 of the selector S. Line relay 25 energizes and closes a circuit for the slow-to-re'lease relay 26. Relay 26 energizes and opens the circuit ot the release magnet 32 and prepares a circuit 'for the vertical magnet' 30 at armature 35; and at armature 34 places ground on the release trunk 23, thereby closing the usual holding circuit for the switching relay 6 of the line switch before the slow-tosrelease line relay 7 drops back..

lVhen the subscriber at substantion A dials the digit 9, the circuit of the line relay 25' is opened a corresponding number of times. Each time the line relay 25 falls back, in response to an interruption. a circuit is closed for the vertical magnet which may be traced from ground by way of armature 41 and its resting contact, armature 33 and its resting contact. armature 35 and its working contact, winding of relay 27,v through the winding ot the vertical magnet 30 to battery. By the operation of the vertical magnet 30, the switch wipers 48, 49 and .59 are raised opposite the ninth level of bank contacts. lThe series relay 27 is energized in series with Vthe vertical magnet, retaining from this same ground potential and close its armature attracted throughout the ver'- tical movement of the switch wipers. As a result, a. circuit is closed from ground "on the release trunk 23 by way of armature 36 and its working contact, normally closed springs 441, oli' normal spring 44 (which are closed `upon the iirst vertical step,), winding of stepping relay 28 to battery. The stepping relay 28 yenergizes and closes a locking circuit for itself at armature 3 7, and at armature 38 prepares the circuit for the rotary the wipers 48, 49, and 50 Vinto engagement with the iirst yset of :banlrcontac'ts in this selected level, and, near the end of its movement, opens the circuit for'the stepping relay 28 at interruptor,contacts 43. The stepping relay 28y now deenergizes and opens the circuit for the rotary magnet at armature 38. The rotary magnet, in turn, deenergizes and again closes its interrupter contacts 43. In case the trunk terminating in the first set oft bank'contacts isidle,:switch ing relay 29 energizes immediately. Assuming the ,trunkv to be busy, however, switching relay 29 is sllort-'circuited by the `ground potential encountered by--test wiper Stepping relay `28 will again energize -a circuit for the' rotary magnet 31a second time.- Thekswitch wipers are thus rotated into engagementl with the second set oit bank contacts. This alternate operation of' stepping relay 28 and rotary magnet 31 continues until an idle tru-nk is reached, which will be assumed'to be the trunk terminating in thebank' contacts 64, 55, and 56. Switching relay 29, beingno` longervshort ci-rcuited by a ground on the test wiper 49, energizes in series with thel stepping` relay 28. not energize at thistirne on account of the high resistance of the switching relay 29. The operation of the switching` relay 29 opens apoint inthe test circuit and prepares the holding circuit' at armature 40;y dis'con` nects .ground'ffrom armature 33 of the line relay at-ar'mature' 41; andV at armatures 39 and 42 disconnects conductorsv 21 and 24V from the Vupper and lower windings of the linie relay and connects'them, by way of wipers 48 and 50 te theupper and lower .windings of the line lrelay 31 ofthe trunk circuit TG1, respectively. The line relayv V81 closes a circuit for the release relay 83 at its armature 84. Upon energizing, the releaseA relay `33 completesa circuitfor Vthe callsignal lamp L at armature 87 places ground on the releasel trunk 62 at yarmat-u-re 86; and at .armature V823 places 4rjpfolllitl on .the

The stepping' relay 28, however, does- Tlll() i of jack J', windingof the cut-olf relay 82 to battery. Cut-off relay 82 energizes and opens the circuit ofthe lamp L at armature 85, thereby extinguishing the lamp L'. Inserting the plug P into the jack J places ground on the sleeve of the jack J at spring 89 and its working contact. Therefore, the discriminating relay 103 remains deenergized at thistime on account of the ground on both end-s of its winding.

When the key K is thrown to the listening Zposition, a circuit-'is' closed from ground by way ofthe resting contact of armature 128 and said armature, the working conta-ctof spring 137 and sai-d spring, upper winding of the lock-up relay 101 to battery. Relay 101 energizes and bridges the attendants head-set across the heavy talking concluetors 153 and 154 at armatures 112 and 114; and at armature 113 closes a holding cir- Y cuit for itself vfrom ground by way of the lower winding of relay 101, armature 113 and its working contact, working contact of spring 138 and said spring, resting contact of spring 131 and said spring, winding VVof the slow-to-release relay 108 to battery. Relay 108 energizes and opens the initial energizing circuit of relay 101 at armature 128. By the removal of ground from armature 128,110 other cord can be connected to the headset at this time, even though the operator inadvertently or otherwise manipulates-the listening key of another cord.

The attendant may now converse withthe subscriber at the calling substation A and Vinquire for the number of -the substation with which connection'is desired, which has been assumed to be the common battery substation B.

Since the line to substation B terminates in the one jack J 5, the busy or idle condition is indicate-d tothe attendant by a plug of a cord being in or not in the `iack J5.

Assuming that the line to substation Bis idle, the attendant insert-s the calling plug P into the jack J 5. InsertingA the plug P into the jack J5 completes a circuit from ground through the lower4 winding of switching relay 107 of the cord circuit CC, sleeve of the plug P', sleeve of jack J5, through thewinding of the cut-off relay 210 to battery. Switching relay 107 energizes and-connects its upper holding Winding to the conductor 15,3 at armature 127 closes a circuit for the supervisory lamp L4 at armature 124'; and at armatures 125 and 126, connects the talking -strands of the Vcord to the tip an-d ring of the plug P', respectively. The tip of the plug P' is also disconnected from the busy test rela-y 109 at the normally closed springs controlled by armature 125. The cut-off relay 210 also energizes and disconnects the line relay 211 from the line conductor-s 217 and 218 at armatures 212 and 213, respectively. f f

The attendant now throws the key K to the ringing position momentarily tov signal the calledy subscriber at substation B.v When the subscriberl at substation B removes his receiver, a bridge is placed across theline conductors 217-and 218, thereby closing a circuit for the battery feed relay'106. Re-

lay 10G, upon energizing, opens the circuit p for the supervisory lamp L4r at armature 123, thereby extinguishing the lamp L4. rfhis indicates to the attendant that the called party has answered. The subscribers may now hold conversation. At the termination of the conversation, both subscribers will replacetheir receivers.

Replacing the receiver at the substation B opens the bridge across the conductors 217 and 21:8, thereby openingV the circuit for the battery feed relay 105. vRelay 106 releases and again closes the circuit for the supervisory lamp L4.. The lamp L4 is again lighted indicating to the attendant that the called party has replaced his receiver.

Then the receiver at substation A is replaced, the bridge across conductors 4 and 5 is opened, `thereby opening the circuit of the rline relay 81 ofthe trunk circuit T C'. r1`he line relay 81 deenergizes and open-s the circuit for the release relay 83.., Bela-y 83 deenergizes and removes zground from the holding conductors 62 at armature 86, and also removes ground from the working contact of spring 89 at armature 88. The discriminating relay 103 of the cord circuit CC is no longer shunted by ground on both ends of its winding, and therefore operates in series withl relayl 82. The function of the operation Vof relayr103V at this time is to close the circuit of the supervisory lamp L3 at armature 116. The lightingof the lamp L3 indicates to the attendant that the call.- ing subscriber at substation A has also replaced his receiver. The attendant is thus signalled by a separate lamp when either the calling subscriber or the called subscriber replaces his receiver, thereby giving what is commonly known as double-lamp switchhook supervision. .Y

' The removal of ground from conductor removes the holding ground from conductor .23, breaking the holding circuit of relay 29 of the selector S, and also of the switching relay 6 of line switch LS. Switching relay 29, upon deenergizing, closes a circuit for the release magnet 32 from ground by way of armature 4:1 and its resting contact, arma.- ture 33 and its resting contact, armature 35 and itsresting` contact, closed oil normal springs 45, through the winding ot the release magnet 32 to battery. Therelease magnet 32 energizes and restores the selector back to normal.

When the operator receives the signals to release the connection by the lighting of lamp L3 and also L4, she removes the plugs P and P" from the jacks J and J5, respectively. The circuits torthe discriminating relay 103 and for the switching relay 107 ot the cord circuit CC, and for the cut-oli" relay V82 of the trunk circuit TC are thereby opened, and all the apparatus is restored to normal.

The assumption is now made that the subscriber at the substation A desires connection with a certain subscriber whose line terminates at one of the common battery manual switchboards. The subscriber at substation A will call the attendant in the manner identical with that described hereinbefore, the call extending through the line switch LS, a selector, such as S, over a trunk terminating in a ack at theattenda'nts position, such as jack J1.l In response to the lighting of the call signal light, the attendant inserts the answering plug P into the answering jack and throws the key K into the listening` position, and inquires for the number of the substation with which connection is desired. After receiving this information, the attendant inserts the calling plug P into the jack of an idle trunk extending to the proper common battery manual switchboard. It will be assumed that the trunki'comprising conductors 229 and 230 accessible at the jack JG and terminatingl in the common battery manual switchboard at the jack J7, is the trunk selected. Y f

'Inserting the plug P1 into vthe jack J6 completes a circuit for the switching relay 107 and the cut-off relay 250 in series. Re lay 107 operates and connects the talking strands to the tip and ring et the plug` P1, respectively, and closes a circuit tor the supervisory lamp L4. Relay 250-operates and disconnects the line relay 251 from the talking conductors 227 and 228 of the trunk circuit TCat armatures 251i and 255,- respectively.

The attendant may now throw the key li to the. ringing position for a short interval, thereby actuating the drop signal 311 at the common battery manual switchboard. ln response to this signal the manual operator will insert/the answering plug of a cord into the jack J7. Battery potential on `the sleeve of the manual operators cord will energize the cut-oli relay 310, thereby open- -ing the circuit for the drop signal 311 at armature 312. Inserting the answering plug into the jack J7 also completes a circuit'for relay 253, there being ground and battery potential on the tip and ring of the manual operators cord, respectively. 253 operates and closes ak bridge including the winding'ot thepolarized relay 252 across conductors 227 and 228 at armature 258. This closes a circuitl for the battery feed relay 106 and the polarized relay 252, in series. circuit for the supervisory lamp L4E at armature123. The lextinguishing of the lamp L4 signals the attendant that the manual operator has answered the call. The polarized relay 252 operates and short circuit-s the greater portion of the winding of the relay 253 at its armature 257. As a` result, the current Vtlow in conductors 229 and 230 is increased suliiciently to operate the super-V visory signal in the manual operators cord.

This latter operation has utility in disconnection and in a call originated vby the manual operator which is to be described hereinafter. The attendant may now converse with the manual operator, informing her of the connection desired, after which she may restore the .key K to normal and proceed tov complete other calls or perform other duties. t

If for any reason the manual operator is unable to complete the desired connection, she may so inform the `calling subscriber directly. It is assumed, however, 'that the manual operator completes the desired connection, after which the two subscribers hold conversation.

After the termination of the conversation, both the automatic subscriber and the called manual subscriber replace their receivers. VVT lien the automatic'subscriber replaces his receiver, the lampL3 of the attendants cord CC is ligted as previouslydescribed. In the vcall being describech'the attendant at the private automatic exchange is the originating operator and therefore removes the plugs P and P trom the jacks J1 and JG, respectively, in response to the lighting ot the one lamp L3. Removing the plug P 'from the jack J6 opens the circuit for the sleeve relay 250. Relay 250 deenergizes and closes a circuit including the bridge across conductors 227 and 223, armatures 2541- and 250 and their resting contacts, the upper and lower windings of line relay 251 to battery and ground, respectively. lt will be noted that the relay 251 ieeds battery potential to the tip side oit .the line and ground potential to the ring side of the line, which is the reverse of the battery feed as was supplied by relay 10G or the cord CC. The polarized relay 252 is caused to drop back and open the short-circuit from the major portion ofV the winding ot relay 253. This reduces the current imvin conductors 229 and 230 sufeiently to light a supervisory lamp in the Relay i Relay 106 operates and opens the manual operators cord circuit, therebyrgiving the manual operator the usual discenvrnect signal. In this kind ot call, i. e., `'from the private automatic exchange to the manual exchange, 1t is usual for the manual operator to wait for the disconnect signal from the private automatic exchange attendant before pulling down the connection. Should the manual operator remove her plug from jack J7 before she receives the disconnect signal, the private automatic exchange attendant receives the additional signal by the lighting of lamp Lt, as will be explained hereinafter.

As has been stated before, substations in the unrestricted class, such as substation A, are allowed outside service; i. e., service to the main automatic exchange. It will new be assumed that the subscriber at substation A desires connection with a subscriber inthe main automatic exchange. y In order to originate such a call, the subscriber at substation A must call the operator by removing his receiver and dialing the digit it being remembered that trunks to the attendants switchboard reserved it'or outside service are accessible in the tenth level of the selector banks. When the calling sul'- scriber at substation A removes his receiver', a bridge is placed acrossthe conductors 4 and 5, which completes the circuit tor the line relay 7 ot' the line switch LS. Line switch LS operates in the hereinbefore described manner to select a trunk to an idle selector switch. Assuming the trunk comprising conductors 21-24, inclusive, is the trunk selected, the line relay 25 and the release relay 26 of the selector S energize and prepare the selector tor operation.

In response to the digit 07 dialed by the subscriber, the selector raises its wipers opposite the tenth level, and then rotates its wipers to select an idle trunk extending to the attendants switchboard.

Assuming that the trunk comprising` conductors 57, 58, and 59 is the trunk selectet a circuit isclosed for the line relay of the trunk circuit TC, which may be traced from ground by way ot armature and its resting contact, conductor 59, over the talking loop to conductor 57, resting contact of armature 7 9 and said armature, through the winding o1 the relay 75 to battery. Relay 75 operates and closes the circuit for the call signal lamp L at armature 7 7 and its working contact` and places ground on the holding conductor 58 at armature 78 and its working contact.. In response to the lightingot lamp L7 the attendant inserts vthe plug'P into the jack J and throws the key K in the listening position, thereby bridging the attendants headset across the talking strands ot the cord circuit. Inserting the plug P into the `jack J, completes the circuit tor the cut-ott relay 7 6 and the discriminating relay 103 in series'. Relayv76 operates to open the circuit et' relay 75cat armatures79 and 80. Relayv75, Yupon deenergizing, opens the circuit tor the call signal lamp L at armature 77 and removes the initial ground from the holding conductor 58 at armature 78. supplied to conductor 58 at armature 80 beiere the lin-e relay 75, being slow acting, has had time to tall back. The discriminating relay 103 operates and places ground on the discriminating conductor 153.21t armature 116 and its working Contact, and at ar-` matures 117 and 118 and their -.vorking contacts bridges the battery feed relay y102 across the talking strands 153 and 154 of the cord circuit. Relay 102 operates'and opens the circuit `for the supervisory lamp L3 at armature 115, thereby preventing this lamp from lighting at this time. The attendant now converses with the calling subscriber and is informed oi' the number ot the substation with which connection is desired. Having received this information, the attendant inserts the plug P into ajack ot an idle trunk extending to the automatic exchange. It will be assumed that the trunk ot spring 206, thereby Apreventing the op-V eration of relay 107 at this time. Cut-ott relay 201 operates and opens a point in the circuit of the supervisory lamp' L5 at armature 203, and connects conductor 208 to the ring` of jack Jl at armature 204 and its working contact, thereby also disconnecting the ring-down relay 202 from conductor 208.

After inserting the plug` P into the jack J, the attendant throws the key K into the dialling position. A .circuit is thereby closed for the switching relay 107 trom ground on the discriminating conductor 15s', spring, through the winding oi' relay 107 to' battery. Relay 107 operates and closes a holding circuit for itself at armature 127 and its working contact; connects the :talking Vstrands of the cord CC to the tip and ring .ot the plug P, at armatures and 126, re'- spectively; and at Yarmature 124 closes a cirworking contact of spring and said A holding ground is cuit for the supervisory lamp L4, thereby also closing the polarizing circuit for the upper winding ot relay 105. The attendants dial D is now bridged across the tip and ring of the plug P at springs 143 and 144 and their working contacts. A circuit is also closed at spring 145 and its Working Contact for relay 104. Relay 104 operates and closes a locking circuit foritself at armature 121, and at. armatures 119 and 120 bridges the lower winding of the polarized relay 105 across the talking strands 151 and 150 of the cord circuit CC.

Vhen the key K is thrown to the dialling position, thereby bridging the dial D across the vtip and ring ot the plug P, a circuit is closed for the line relay ot the line switch LS2 at the distant main automatic exchange. rPhe line switch LS2 operates and selects the trunk to an idle selector, the manner of operation being similar to. that of line switch LS described hereinbet'ore. Assuming the trunk comprising conductors r301, 302, and 305 is the selected, the line and release relays of a corresponding selector operate to prepare the said selector for operation and also ground the release trunk 302, thereby completing the holding cii'cuit for the switching relay otl the line switch LSZ. In response to the digits 'dialled by the attendant, this selector, and possibly others, as the case may be, and a connector, operate to eX- tend the connection to the desired substation and ring the bells. Aiter dialling the number of, the called station, the operator restores the key K. .Y Y

`Whcn the called automatic subscriber removes his receiver to answer the call, the direction ot current. over the calling trunk is reversed by the operation of the backbridge relay of the connector switch at the main automatic exchange, as is well known in the art. rPhis reversal of current causesV the polarized relay 105 of the cord circuit, which is now bridged lacross the calling trunk con ductors 207 and 208, to operate and open the circuit Jfor the supervisory lamp L1 atv armature 122. The extinguishing of the lamp L4 indicates to the attendant that the called automatic subscriberhas answered and that the two subscribers are holding conversation.

Then the conversation is completed, both subscribers will replace their receivers. When the called subscriber replaces his receiver, the direction of current iiow over the calling trunk and, therefore, in the lower winding of the polarized relay 105 is reversed back to normal by the cle-actuation ot the back bridge relay in the connector switch. Relay 105 fallsk back and again cioses the circuit for the supervisory lamp L4 at armature 122. Y la* signals the operator that theealle'd subscriber has replaced his receiver. o l When the calling subscriber at substation A replaces his receiver, the bridge across tlielieavy talking strands is opened, thereby opening the circuit Jfor the battery feed relay 102 in thecord circuit. .Relay 102 deenergizesand again closes the circuit tor the supervisory lamp L3 at its armature trunk ner described hereinbefore.

The lighting ot lamp.

115.Y The lighting ot lamp La signals, the at'- tendantfthat the calling subscriber has replaced hisreceiver'. i. .Y

'Phe lighting of bothilamp L3 and lamp L? is the disconnect signal for the attendant, in response to which she removes the plugs P and P trom the jacks J and J *,respectively. Removing the plug P from the jack J4 opens the circuit for the cut-olfV relayv 2,01,

and opens the holding bridge across the conductors 207 and 2,08." `The selectors, and connectors in the niain automatic exchange are now released -in the usual ,manner.

Ground isy removed from the holdingnconductor 302, thereby .openingA the `holding Vcircuit tor the line switch LS?, restoring it to normal.

Removing the plug P from the jack J opens the circuit ytor the cut-oit relay 7.6 and 1 the discriminating relay 103,l `Relay 103 deenergizes and'removesground from the discriminating condu'ctoril at armature 116'. The removal of ground from the discriminating conductor 153 opensvthe holdiiigcir.-

cuit ofl the switching relay 107, and opens the circuit for the lamp L?. Relay 107 falls backy and openslth'e circuit torglamp L4 and the polarizing winding of relay 105, at ar mature 24 'andl disconnects V the talking strands from tlie'tipand ottlieplug P at armaturesl125 and12,respectively. Relay 76 deenergizes and removes Alground from the holding conductor 58 vat armature 80. kThe removal ofgroundfi'rom the hold.-

ing conductor causes the release ofthe .selector S and the line switch LS in the .man-

y In theforegoing,descriptions, ytlie operations for completing connections vfrom alpsubstation in theunrestricted class toma substation at the ,mainautomatic exchange, to one of the individualv common battery ,telepophones, and to a substationTotl ,one ofthe common ybattery manual swi-tcliboards,` are described. As previously mentioned-'inthe beginning of this speciication.,y the substations having restricted service vmay, alsoobtain connection with any of the individual comm-on batteryk telpehonfes or with any ol the substations of the common battery manuall switchboards. `Connection between a restricted substation such as A and an individual common battery substation, such as B, may be extended by way of the line switch'. LS" individual tothe substation A, a selector, such asv S,Yover a trunk terminatingat the atteudantsswitcliboardin a jack, such as J1', whence the attendant inay complete.y the 'connection by means of a cord CC, to the jack J 5, which is individual to the line to the substationwB. The various operations performedlby the at are identical to lthose h ,ereinbeij'ore described in completing a connection trom the substa-v tendant andalso by the automatic switches the connection desired.

tion A to the substation B. Likewise a connection may be completed from a restricted substation to any of the substations of a common battery manual switchboard'in a. manner identical to the manner in which a connection is completed from the substation A to any of the substations of the common battery manual switchboard.

In order to further bring out the features of this invention, it will now be assumed that the subscriber at substation A attempts to obtain connection with a substation at the main automatic exchange. It will be remembered that since the substation A is assigned to restricted service, this connection isnot tov be granted. In the following descriptions, it will'be shown how any attempts to complete an unauthorized connection will fail. In an attempt to obtain such a connection, the subscriber at A may either dial the digit 0, it being remembered that trunks to the operators position reserved for service to the main automatic exchange are accessible in the tenth level of the selector banks, or he may dial the digit 9, thereby complet-ing a connection with the operator in the manner previously described and then instruct the operator to complete It will be assumed first that the former attempt is made. lVhen the subscriber at A removes his receiver, a bridge is placed across conductors 4L and 5, which completes a circuit for `the line relay `6 of the line switch LS. The line switch LS, as described before, operates toselectI a trunk to an idle selector. Assuming the trunk comprising conductors 21-24, inclusive, is the trunk selected,vthe line relay 25 andthe release relay 26 of the selector S, enf ergize and prepare the selector for operation.

The subscriber rat A now dials the digit 0. In response to the impulses produced, the selector raises its wipers opposite the tenth level of bank contacts. 'lVhen the shaft supporting the Wipers is raisedto the tenth level, the shaft springs 96 are closed, thereby 'placing ground upon the test wiper 49 by way of jumper 16, working contact of armature lO, and said armature, wiper I8 and contacts 97, closed springs 96', to wiper 49. It will be remembered thata. busy trunk is denoted by ground upon the' test contact. Therefore, when the selector begins its roi tary trunk selecting movement, in eifect all trunks will test busy, and the wiper willbe rotated over the entire level to the eleventh contact set. On the eleventh rotary step the cam 94 opens the circuitof the stepping` relay 28 at the springs 44, and also closed the springs l46 and 47, thereby removing the original ground from the lower windingv of the line relay 25, and substituting the ground from the busy machine B. The busy tone is thereby superimposed upon the conductors 24 and 2l which indicates to the subscriber at substation A thatthe attempted connection is not being completed. l

The method employed to viestrict the service at any substation now becomes evident. In the individual line switch of any restricted substation, for example, the line switch LS of the substation A, ground is connected to the working contact of the armature l0 by means of the jumper 16. Direct ground is thereby placed on the test wiper of the selector whenever theshaft springs 96 are closed, the assumption in this case beine` that they are closed when the selector shaft is raised to the tenth level. In the individual line switches of the substations granted unrestricted service, for example, line switch LS of the substation A, no ground is connected to the working contact and. armature l0, the jumper being omitted. Consequently, the armatures corresponding to armature l0 and the wipers corresponding to wiper 18 have no function on these line switches, and the unrestricted substations can obtain connection on all levels of the selectors.

It will now be assumed that the" subscriber of the restricted substation A attempts to obtain connection to a subscriber in the main automatic exchange by calling' the operator in the usual way by dialling vthe digitr 9 and then requesting the `desired connection. When the attendant answers the call in the usual manner, the subscriber lat the substation A gives her the number of the 'desired substation at the main automatic exchange. The operator takes notice that the call is con'iing in over a trunk not permittedout- 'side service in the main automatic exchange. She then refuses to set up the connection and informs the'calling subscriber laccordingly. y Y

Should the operator overlook the fact that the call is coming in overa trunk not assigned to outgoing service to the main auto matic exchange, she may attempt to complete the connection by inserting the calling plug of a cord CC into the jack of an idle trunk to the main automatic exchange. lt is assumed that the trunk comprising .conductors'QOT and Q08 terminating in the jack J is the trunk selected. Inserting the plug P into the jack .I1 allows the cut-olf relay 201 to operate from' ground on the make contact ofy spring 20G. Switching relay 107 does not energize over its lower winding be` cause of the ground on both ends -of this winding. The attendant -throws the key K to the dialling position in an, attempt to dialv the number of the desired substation. It will be remembered, however, that when the plug P is inserted in a jack, such as J, in answering a call, the discriminating relay 103 is maintained inoperative because of the ground on the 'working contact of spring 89. Therefore, no ground potential is supplied lUU llt)

to the discriminating.conductor 153. Consequently, no circuit will be closed at spring 146 and its working contact tor the upper winding of relay 107. vSince neither the upper winding nor the lower winding ot relay 107 is energized, relay 107 does not operate andthe actuation ot the dial D is et no avail, since the talking strands ot the cord circuit are disconnected from the tip and ring of the plug P at the armatures 125 and 126, respectively. The circuit lor the supervisory lamp L4 is not closedat armature 124, and the failure ot the lamp L* to light indicates to the attendanty that the attempted call is notbeing completed, whereupon she will recall the tact thatY service is to be denied and will inform the calling subscriber accordingly. Y

ln accordance with a special feature 'of this invention, it will now be shown how it is impossible 'tor the attendant to complete the unauthorized connection in question, should she deliberately attempt to complete such a connection. ln vthe foregoing para graph, it is shown how the unauthorized connection being attempted cannot be completed by `inserting the answering plug l* and calling plug P of the cord circuit CC into the jacks J and 5*, respectively, thel reason being that relay 103 is short circuited by the ground at the spring 89 when plug P is in jack J; and, therefore, no ground is supplied to conductor 153 to energize relay 10",7 when the dialling rey is depressed.`

Consequently, the connection is held open at arniatures 125 and 126 ot relay 107.

twill again be assumed that the subscriber at substation A has called the attendant byy dialling `the digit 9 and that the attendant has answered by inserting the plug P into the jack J and that the attendant has received the number of the desired substation. ln order to call thewdesired substation at the main automatic exchange, the attendant may attempt to use a second cord. By inserting the answering plug ot the second cord into any idle outgoing trunk jack, such as J, and inserting the calling plug ot the second cord circuit into au idle trunk to the main automatic exchange and by dialling the number of the called substation, the attendant mayV obtain connection with the called substation in the ordinary manner. The relay in the second cord circuit similar to relay 103 energizes in series with relay 70, and the relay similar to relay 107 operates in response to the actuation et' the dial rey `trom ground on the conductor similar to 153/. The attendant may now throw both the lzey l and thelistening key ot the second cord circuit in the listening position in an attempt to complete the connection by means ot the twoy cord circuits through'the attendants head set. This attempt will tail, however, because, soon as the listening keys of the ytwo cords are thrown, vthe ground on the spring l89is conducted by way ot the sleeve ot jack J sleeve of plug P, working contact et spring 139 and said spring, to the associated common conductor and through the spring and its working con-y tact olfy theisecond cord circuit similar to spring 130 Vand itsworling contact to the winding ot the relay in the second cord vcircuit similar to relay 103, This relay is thus short circuited and deenergized. Ground'is removed trom the conductor in the second cord circuit similar :to 153, andthe relay in the second cord circuit similar to relay 107 is deenergized. The yconnection ,is then opened at the armatures ot' thisrelay in the second4 ,cord circuitl lsimilar tov relay 107. The resulting condition soon becomes apparent to the, attendant who,'realizing that the unauthorized connection cannot becomingly. Y .i

'lhere is also another reason why the above attempted connection cannot be completed in that only one cord circuit can be connected tothe attendants,headset at one vbeen shown that it is impossible, to complete a call from a restricted substation to the main automaticexchange- Inthe following description, it will, be shownv how calls originating at either a common battery manual switchboard or a common battery telephone may be extended to any substation in the private automatic exchange; and also how. calls originating at the main automatic exchange may be extended to any of the private automatic substations allowed unrestricted service.l n l 'lo complete a call from a common battery manual telephone, such as B, to any ot' the private automatic substations, the subscriber at substation B removes his receiver to call the operator. `Removing the receiver at the substation Bcloses a bridge -across the conductors 217 and 218, thereby completingy a circuit tor the line relay 211 by way ot varmatures 212 and 218 and their resting conthe talking strands 153 andfle ot `the cord.

i pletcd, informs the calling subscriber accord- CC. inserting the plug P into the jack J 5 closes a circuit for the discriminating relay 108 and the cut-olf relay 210 in series. Relay 210 operates and ope-ns the circuit .for the line relay 211 at its armature 212 and 213. The line relay 211 deenergizes, thereby extinguishingfthe lamp L. Relay 103 operates and placesground potential on the discriminating Vconductor 158 at armature 116, and bridges the battery feed relay 102 across the talking strands 1511 and 153 of the cord circuit at armatures 117 and 118. Relay 102 operates and opens the circuit for the supervisory lamp L3 at the armature 115. Talking battery lis furnished to substation B through relay 102.

The attendant now converses with t-he calling subscriber to Aobtain the number of the private automatic substation with which connection is desired. 1t will first be assumed that the substation with which connection is desired is the unrestricted substation A, having the multiple jack J2 at the attendants switchboard. Before insertingthe plug P into the jackJz, the attendant will touch the tip of the plug P to the sleeve ofthe jack J2 to determine whether the substation A is` busy or idle. lIf the subst-ation A .is busy, a circuit will be closed from ground on conductor 66', conductor sleeve of jack J 2, tip of plug 1', normallyr closed springs controlled by armature 125, through the vwinding of the busy-test relay 109 to battery. Relay 109 operates and closes a circuit at armature 129 for the tertiary winding of the inductance coil of the attendants head set.' The sudden building up of current in the tertiary winding' induces a momentary flow of current in thev secondary winding of the induction coil, which produces a click in the attendants receiver. rlhis click in the attendants receiver indicates that the substation A iis busy. assuming that the substation A is idle, no click will be heard in the. attendants receivei and the attendant will proceed to insert the plug P into the jack J 2. A circuit will be closed from ground by way of the lowerY winding ofthe relay 107 sleeve of the plug P, sleeveof jack J2, conductor 66, conductor 66, winding` of the switching relay 6 of the line switch LS, resting contact of armature 15 and said armature, winding of stepping magnet 8 to battery. On account of a mechanical interlocking device controlled by the armature of the line relay l, which is now normal, the armatures of the switching relay 6 are attracted only enough to disconnect the line of the substation A from its normal battery and ground connections in the lineswitch LS. Switching relay 107 operates over its lower winding and closes a circuitfor the supervisory lamp L, connects the talking strands of the cord circuit to the tip and ring of the plug 13 aereas@ respectively; and closes a holding circuit for its upper winding, as previously described. To signal the subscriber at the substation A, the attendant intermittently throws the key K to the ringing position and back to normal, thereby ringing the bells at the substation A.

lVhen the subscriber at the substation A removes his receiver, a bridge is placed across the line conductors land 5, thereby completing a circuit for the battery feed relay 106 of the cord circuit CC. Relay 106 operates and opens the circuit for the supervisory lamp L4 at its armature 123. Relay 106 also supplies talking battery to the called substation A. The extinguishing of.

the lamp L4 indicates to the attendant that the called subscriber at substation A has answered and that conversation is being held.

l-.V hen the conversation is completed, both subscribers will replace theirr receivers. Replacing the receiver at substation A opens the bridge across the line conductors t and 5 which opens the circuit'for Vthe battery feed relay 106. Relay 106 deenergizes and again closes the circuit for the supervisory lamp L4. The replacing of the receiver at substation B opens a bridge across the line conductors 217 and 218, thereby opening the circuit for the battery feed relay 102. Relay 102 deenergizes and again closes the circuit for the lamp L3. The lighting of lamps L3 and L4 indicates to the operator that she may pull down the connection.

It is now assumed that the subscriber at substation B desires connection with the restricted substation A, having the multiple jack J 3 at the attendants switchboard. i'

The subscriber at substation B lifts his receiver to call the operator and gives her the number of the substation with which connection is desired. Before insertingl the plug P into the jack J 3, the attendant Vtests the line in the manner described above. Assuming the substation A is idle, the attendant inserts the plug P into the jack J 3. A circuit is again closed from ground by way of the lower winding of the relay 107, sleeve of plug P, sleeve of jack J3, conductor 71, conductor 71, the switching relay and stepping magnet of the line switch LS to battery. The switching relay of the line switch LS operates to disconnect the line conductors 2 and 8 from their normal battery and ground connections in the line switch LS in the manner described hereinbefore. The lower winding of the switching relay 107 is not energized at this time because of the ground on the working Contact of the springs 91 of the jack J 3.

rEhe attendant now signals the subscriber at substation A by intermittently throwing the key K to the ringing position. As soon as the key K is thrown to the listening po- Ill;

sition, a circuit is yclosed from ground on the discriminating conductor 153 by Way of the Working contact of spring 1112 and said spring, through the upper Winding oi the relay 107 to battery. Relay 107 nonT en# ergizes and immediately closes a holding circuit for itself at armature 127, and prepares the ,co-rd circuit as described hereinbefore. When the subscriber at substation A removes his` receiver, a bridge is placed across the line conductors 2 .and 3, thereby closing a circuit through the'bat-tery feed relay 106. Relay 106 operates andopens the circuit for the supervisory lamp L4.

When the conversation is completed, both subscribers will replacetheir receivers and the attendant will receive the disconnect signal by the lighting of lamps L3 and L4, whereupon sheproceeds to pull down the connection. f y

Calls may also be extended from any of the subscribers of the common battery manual switchboard to the subscribers of the' To complete' private automatic exchange. this kind' of a connection', the subscriber of the common battery manual switchboard rstcalls the manual operator by removing his receiver. VIn response to the usual signal,

the manual operator answers the call and proceeds to complete the connection by inserting the calling plug oit one .or her cordsv into the jack yot an idle trunk extending to the private automatic exchange. Assuming this ltrunk to be' the lone comprising conductors 229 and 230,v the manual `operator inserts the callingplug of her rcord into the jack J. The cut-oli relay 310 'is energized; from battery on the sleeve of the operators cord and operates to open the circuit of the drop-signal relay 311 at' armature 312. Since there is ground and batt-ery potential presenten the tip and ring or the manual operators cord, respectively', inserti-ng the plug of the operators cord into jack J7 sup plies current to conductors 229 and 230.` and closes a circuitlfor the relay 253. Relay 253 operates and closes a circuit for the l-ine relay 251 and the polarized `relay 252 inV vseries at armature 258. Relay251 operates and closes a circuit for the call signal lamp L7 at armature 256. The flow of current in theypolarized relay 252 at this time is in such a direction so as to maintain relay 252 inoperative.

In answer to the lighting of theplainp L7', the attendant inserts the answering plug P ot' the cord CC into thel jack J6. As are? sult, a circuit is closed for the discriminating relay 103 and the cut-olif relay-250 in series. Cut-off relay 250 operates and disconnects the line relay 251 from the conductors 227 and 228 at armatures 25a and 255, respecq tively. Line relay 251 deenergizes and extinguishesthe lamp L7. The discriminating relay 103 operates and places groundv on the discriminating conductor 153 at `armature 116- and bridges the battery reed relay 102 across tlie talking strands 153 and 1.541 oli' the cord CC inthe usual manner. Battery feed relay 102 noW operates and opens the circuit itorthe supervisory lamp at armature 115. Ground! and* battery are 'now supplied through the battery e'edrelay 102 to .thel conductors 227 and 228, the reverse oi' that supplied through `the line relay 251. The current through the polarized,l relay252 is noiv in the direction to cause its operation.

The polarizedr relay 252 operates and short circuits the greater portion of the Winding of relay 253 at the armature 257 and its Working contact. As a result, the current in the conductors 229 and 230 is'suiriciently increased to operate the usual supervisory signal in the operators cord, andl thus signal the manual operator that the attendant at the private automatic exchange has ansvs'lered.` The manual operator 'now informs the atn y tendant at the private automatic exchange of the connection desired, and the attendant proceeds to completev the'connectionto the desired substation of the restricted or the unrestricted class, as the case may be, in the manner described in the foregoing .descrip` tion.

At the termination of the conversation, both the automatic subscriber and the common battery manual subscriber Will replace their receivers. Replacing the receiver at the automatic substation opens the bridge across the talking strands- 151l and 150, lthereby opening the circuit or the loo batteryy feed relay 106.L lRelay 106` deenei'- gizes and closes afcirc'uit for the superisory lamp L4'. When thecommon battery manual subscriberA replace his receiver, thelmanual operator receives the` usual signal and proceeds to remove the plugfrom the jack J7. This opens the circuit for the relay 253. Re` lay 253 deen'ergizes andopens the circuit for the battery feed relay 102. Relay 102 deenergizes and' closes the circuit for the super"V visory lamp L3. The lighting or both lamps L? and L4t is the disconnect signal to the attendant in response to Which she pulls y down the connection.

Calls originating at the main Yautomatic n restricted class at the private automatic exchange, such as substation A..A To originate the call, the `subscriber at themain automatic 1 exchange removes his receiver and dials the directory number assigned tov the-private automatic exchange. The call Will be ex? 'as described liereinbetore.

f tall back to normal.

. switch LS in series.

tended in the usual manner through a line switch, one or more selectors, and to a rotary connector in the banks of which access is had to trunks extending to the private automatic exchange. r iter the subscriber at the main automatic substation has finished dialling the last digit, the rotary connector automatically selects an idle trunk extending to the private automatic exchange and supplies ringing current thereto. Assuming the trunk comprising conductors 207 and 208 accessible at the bank contacts 310, 311, and 312, is the trunk selected, the ring-down relay 202 becomes energized by the ringing current and locks up mechanically by an interlocking arrangement (not shown) controlled by the armature ot the cut-ott relay 201. Ground supplied to contact 311 by the rotary connector completes a circuit for the switching relay-ot the line switch LS2. The switching relay operates sutciently to disconnect the trunk conductors 207 and 208 from the line switch LS?. The ring-down relay 202 `operates and closes a circuit tor the lamp L5 at armature .205. The lighting` ot lamp L5 signals the attendant who answers the call by inserting the answering plug P of the cord int-o the ack JL1 and threwing the key K into the listening position in the usual manner. The subscriber at the main automaticl exchange may now intorm the attendant of the substation with which connection is desired. Inserting the plug P into the jack J L closes a circuit tor the cutoii 'relay 201 andthe discriminating relay 103 in series.l Relay 103 is prevented from operating on account of the additional ground on the sleeve of jack J 4 at the working contact of spring 206, which places aV ground on both ends ot the winding of relay 103. The cut-0H relay 201 operates and opens .the circuit tor the call signal `lamp L5 at arma-ture 203, and also unlocks the armatures of relay 202, allowing relay 202 to 1 Cut-off' relay 201 alsol disconnects trunk conductor 208 from relay 202 and connects it to the ring of the jack J 4 at armature 204. Since it has been assumed that the private automatic substation with which connection is desired is the substation A, the attendant will insert the callingpluor P ot the .cord into the multiple jack J2 This closes a circuit for the switching relay 107 and .the switching relay 6 of the line Y The switching relay 6 operates sufficiently to disconnect the line conductorst and 5 from the line switch LS, Switching relay 10T operates to complete the circuit for the supervisory lamp LA1 and to connect the talking strandsot the cord circuit CC to the tip and ring of the plug P', respectively, as hasvbeen previously described. The attendant signals the subscriber at substation A by means of the key K.

When the subscriber at substation A re-y moves his receiver, a direct current bridge is placed across the conductors 4 and 5, there by closing a circuit for the battery feed relay 106. Relay-106 operates to open the circuit for the supervisory lamp L". The subscribers may now hold conversation.

the receiver at the mainautomatic vsubst-ation releases the automatic switches inthe usual manner: c

In previousparagraphs, it hasbeen shown how it is impossible to establish a connec-` 'tien between a restricted substation, such as A', and a substation at the main automatic exchange. Similarly, itis impossible rto establish a connection troni a substation in the main automatic exchange to a restricted sub.-

st-ation at the private automatic exchange. To brieiiy describe the result of an attemptl to complete an unauthorized connection, it

will be assumed that a connection from the mainvk automatic exchange to the restricted substation A is requestechand that the atL tendant attempts to complete this connection by inserting the plug 4P into the trunk jack J4 terminating the trunk over vwhich the call is assumed to be coming, and by inserting the plug P into the jack J3. The discriminating relay 103 is maintained inoperative on account of the ground placed on the sleeve of jack J t at the working contact of springs 206 when theplug'P is inn serted in jack J4. For this reason, no ground potential is supplied to the conductor 153. The lower winding of the switching relay 107 is not energized because of the ground suppliedv to the sleeve of jackJ3 at `spring 91 and itsworking contact, when the plug Pv is inserted into jack 3; ioris it possible to energize the upper winding of 'relay 107 because ot the absence ot ground on the discriminating conductor 153. The connection between the two subscribers is therefore held open' at the armatures 1.25 and 126 of the switching relay 107.

There is another manner in which theattendant maylattempt to complete the uiiaukey K and the corresponding key ofthe. second cord in the listening position in anI eiort to complete the call through the opT `resistance winding.

erators head set. This attempt will fail, however, because only one cord can be connected to the head set at one time. The relay 108 in the operators head set has a high The lower winding of the lock-up relay of each cord, such as the relay 101 of the cord circuit CO, is a low resistance winding. As stated before, the lockup relay 101 is held up by its lower winding which is in series with the winding of relay 108. The resistance of the winding of relay .108 and the resistance of the lower winding of the lock-up relays of the cords are such that while one lock-up relay will hold up in series with relay 108 ofthe attendant-s head set, two lock-up relays in parallel will not fhold up in series with the relay 108. Vlien the operator throws two keys in the listening position simultaneously, the two corresponding lock-up relays will pull up from ground on the resting contact of armature 128 of relay 108. The two lock-up relays operate and close the circuit for the relay 108 at the armatures corresponding to armature 113. Relay 108 energizes ant opens the initial energizing circuit for the two lock-up relays at its armature 128. Since the two lock-up relays are in parallel, each lock-up relay receives an insuliicient current through its lower winding to hold itself operated. The two lock-up relays therefore drop back and open the circuit for relay 108 at the armatures corresponding to armature 113. Relay 108 drops back and again closes the initial energizing circuit for the two lock-up relays at armature 128. This action of the lock-up relays repeats itself .in a. buzzer-'like manner until the at* tendant, seeing thatno connection is being completed, restores the two listening keys, or until one of the two lock-up relays falls back a. sufficient length of time before the other opens its circuit at its armature corresponding to armature 113, to allow the latter lock-up relay to lock up directlyr in series with the relay 108. Only one cord, however, is then connected to the 4head set, which will immediately become evident to the attendant. It is then apparent to the operator that the unauthorized call Cannot be completed,'whereupon she will inform the calling subscriber accordingly. v

A connection may be established from any of the subscribers at the main automatic exchange, to any of the individual common ybattery substations, or to any of the substations of .the common battery manual switchboards. Likewise, connections may be established from substations of the common battery manualswitchboard to any of the substations vat the main automatic exchange, or with any of the individual common battery substations; or 'from the individual common battery substations to substations of the main automatic exchange,`or substations in the commonbattery| manual switchboard; or

between any two `individual common battery substations. The operations performed and the sequence thereof, and the lfunctions of the separate circuits in completing any of Athe above mentioned connections is evident m the descriptions of theyarious operations given in the foregoing paragraphs.

Y. Long distance-serviceis also available to thetindividual common battery telephones, to the substations at the common battery 'manual switchboards, or to the unrestricted substations of the private automatic exchange. any of these substations wishing a long distance connection will call the attendant at the private' automatic exchange and inform her accordingly. The attendant then calls the long distance operator at themain automatic exchange over a trunlrsuch as the .trunk Comprising conductorsg20:7 and 208, in turn informing the long distance operator of the connection desired. When the longy distance operator Vvat the main automatic exchange has established connectionV with the distant substatiomshe vrecalls the attendant at the private automatic exchange over asimilar trunk, suoli asvthe one comprising conductors 207 and 208.V

The attendant at the private automatic exchange now completes the connection by rect ling the subscriber who desires this .long A distance connection. i l l Vlin establishing a long distance call from a subscriber in the manual exchange, it'may be desirable to hold the set-up between the manual operator and the private yautomatic exchange during the time that the long Vdistance operator at the main automatic exchange is extending the call. Then as soon as the long distance operator notifies the attendant that the desired long distant connection has been obtained, the attendant need only resignal the manual operator; A llash key K2 is provided for this purpose. As-

suming then that the plug l is inserted in the jack J6, and .that the attendant at the private automatic exchange wishes to flash the operator at the common battery manual switchboard to whichthe trunk comprising conductors 229 and 230 extends. ril`he attedant willthrow the key K inthe listening position and will intermittently throw the key K2 to the flashing position. Norma ly,

when the plug P is in 'the jack 4J, the diseliminating relay 103` is hield operated tin series with the sleeve relay 250. Battery is then supplied through the battery feed relay 102 to conductors .227 and 228 in the proper direction to operate the pola'ized relay 252. As described above, the supervisory signal in tne manual operators cord is lll) responsive to the action of the polarized relay 252. When the key lis operated to the flashing position, relay 103 is intermittently short circuited by ground at the workn ing contact vot' the springs 132 by way of spring 139 and its working contact. Relay -103 energizes Vand deenergizes responsively, and, as a result, intermittently connects and disconnects the battery feed relay 102 from the conductors 227 and 228. The polarized relay 252 pulls up andv drops back in synchronisin with the operation of the key K2 and thereby causes the lashing of the supervisory lamp in the manual operators cord.

During the flashing period, relay 108, being slow tojrelease, is maintained operated from ground on the working contact of spring 131 and said spi-ing. The first time the holding circuit ot the lock-up relay 101 is opened at spring 131 and its resting contact, relay 101 drops back. Since its initial energizing circuit is held open at armature 128, relay 101 is maintainedAdeenergized during the flashing period. This prevents the impulses produced by flashing from being heard iii the attendants receiver.

' Various other uses of this flashing key will suggest themselves to those skilled inthe art.

lVhatfis claimed is:

1. ln a telephone system, a branch eX- change, restricted and non-restricted lines in said branch exchange, means for establishing a connection between any of said lines, restricted and non-restricted trunks terminating at said branch exchange, means forestablishing` a connection between any ot said trunks and any ot said non-restricted lines, means for establishing a connection between any of said non-restricted trunks and any ot said lines or said trunks, and means tor preventing a connection between a restricted line and a restricted trunk.

2. In a `telephone system, a branch eX- change including a. group of lines, a second group of lines, means including a cord circuit AVfor establishing connections between any of the lines ot the lirst group; between certain ot the lines in the first group and any of the lines in the second group; and between cer-.

tain ot the lines in the second group andany of the lines in the firstgroup, and means for preventing the other lines in the lirst group both from calling or being called by the other lines in the second group.

3. In a telephone system, an operators switchboard, restricted trunks terminating in jacks at said switchboard, non-restricted trunks tcri'i'iinating in other jacks at said switchboard, a cord circuit including a calling plug and an answering plug and having its talking conductors normally disconnected troni said calling plug. a key in said cord circuit, means in said cord circuit tor connecting the talking conductors of said coi'd circuit to said calling plug` upon insertion ot said calling plug into a. non-restricted trunk jack, means in said cord circuit for connecting the' talking 'conductors oi" said cord circuit to said calling plug` upon insertion ot said answering plug into a nonlrc.- strictei'l trunk `Jack and actuation of said key, and nieans ttor prcventiiig` the connection ot the talkingconductors ol said cord circuit to said calling plug upon insertion or' both ot' said plugs into restricted trunk jacks.v

el. ln a telephone systeii'i, trunk lines terininating in jacks, a cord circuit having its talking conductors normally disconnected troni the calling plug thereof, a key'in said cord circuit, means lor connectingsaid talking conductors to said plug responsive to the minals to said cordcircuit, a key and means for energizing said rela-y upon insertion ol said plug into said jack or upon the ope ation of said key independent of the insertion of the plug. Y

6. ln a telephone system,`an operators switchboard, a first trunk line terminating in a Jack, a second trunk line terminating iii a. ljack, a cord circuit having a plug normally disconnected from said cord circuit, a relay in said cord circuit, means for actuating said relay whenever said plug is inserted into the jack of said first trunk line, ii'ieans tor Apreventino' the actuation of said relay whenever said plug is inserted into the ack of the said second trunk line.

7. In a telephone system, an attendants switchboard, trunk lines terminating in jacks, a cord circuit having a calling Aplug land an answering plug, and having 'its talking conductors normally disconnected from said calling plug, a relay having two wind-` ings tor connecting the talking'conductors oit said cord circuit to said calling plug, means for energizing said relay over one winding` upon insertion ot saidV calling pluginto a trunk )ack` means for preparing the circuit ot the other winding ot said relay upon insertion ot said answering plugin a trunk jack, and manually operated means for en` crgizing said rclayover the said other winding provided said answering plug has been inserted in a trunk j ack.

8. ln a telephone system, an operators position, a cord circuit including a plug,`a re lay in said cord circuit having a winding connected to the sleeve terminal ot' said plug and contacts 'in the talking conductors of said cord circuit, a trunk line terminating in a Jack at said operatorls position, another trunk line terminating in a second jack at til) said operators position, means for energizing the winding ot said relay upon insertion oit said plug` into said lirst jack, and nean's for short circuiting the Winding oi said relay upon insertion of said plug into said second j ack. l

9. In a telephone system, a cord circuit including a plug, a relay in said cord circuit connected to the sleeve terminal of said plug, a line terminating in a jack, a relay connected to the sleeve terminal of said-jack, a second line terminating in a second `jack, a relay connected to the sleeve terminalof said second jack, means for operating the relayin said cord circuit in series relation with the relay connected to the sleeve terminal of said first ack upon insertion of said plug intol said irst jack, and lmeans 'for short circuiting the relay in said cord circuit and operating the relay connected to the sleeve terminal of said second jack upon insertion of said plug into said second jack.

10. 'Inf a telephone system, a restricted line, a 'non-restricted line, a cord circuit for extending a connection to either of' said lines, 'said cord circuit having a calling end, a normally closed bridge iii said cord circuit, a` normally open bridge in said 'co-rd circuit, means for opening said lirst bridge and closing said-second bridge, and means for disabling said iirst means depending on Whether said cord circuit is connected to said restricted line or saidnon-restricted line.

11. In a telephone system, a iirst trunk line leading to an automatic enchange, a second trunk line. leading to a `manual eX- change, a. cord circuit for extending a con nection to either of said trunk lines, a normally closed bridge including a relay in said cord circuit, a normally open bridge including a second relay in said cord circuit, means for opening said first bridge Vand closing said second bridge depending on whether said cord circuit is connected to said iirst trunk line or said second trunk line.

12. In a telephone system, an operators position including a. head set and a plurality oi' cord circuits, means including a key, in each of said cord circuits for connect` ing said cord circuit to said head set, and means ,at said operators position for preventing more than one of said cord circuits being connected to said head set at the same time.

13. In a telephone system, an operators position including` a head set and a. plurality of cord circuits, means including a key, Jfor connecting any one of said cord circuits to said head set and for preventing a. plurality oi said cord circuits being simul taneously connected to said head set.

14. In a telephone system, an operators position including a head set, a cord circuit, a relay in said cord circuit for connecting said head set to said cord circuit, manually operated means including a key, fora-closing` an initial'energizing circuit Jfor said relay and a lockingcircuit for said relay, and a second relay included in said locking circuit for openingsaid initial energizing circuit. 15. ina telephone syst-ein, a trunk line terminating in ajack, a cord circuit including af plug, ya normally openy batteryffeed bridge in said cord circuit,`means for closing said bridge upon insertion of said plug into saidH jack, and `\operatorcontrolled meansv for including a listening keyV for dis-- connecting said bridge and reconnecting iti at win. y i

1G. in a teleplioneysystem, a trunk line terminating ina jacln-a cord circuit including aplug, al battery Jreed bridge'in saidcord circuit4 normally disconnected from the talking conductors of saidc'ord circuit, means for connecting said bridge across said trunk line upon insert-ion of said plug into said j ack, andv operator-controlled means including a listening Akeyfor disabling first 4aid means for disconnecting said bridgeand' reconnecting it at `will. A i

'17, In a telephone system, a cordA circuit comprising talking strands and having a' plug at-eacli end, saidhstrands beingnory mally open, and meanson'trolled through I either plug for closing'said strands.I l

1S. in a telephone system, a plurality of groups or" lines, each group containing restricted and unrestricted lines, a cord circuit for connecting lines ot one group With those of another, said cord circuit including talking conductors and having a plug at each end, said plugs being normally in inoperative relationship, and means 'for bringing' them into operative relationship, said means being effective when either ot said plugs is associated with a non-restricted line and the other plug is associated With any line and being ineiiective when both. plugs are associated with restricted lines. v

19. In a telephone system, a restricted and a non-restricted line, restricted and nonrestricted trunks, a cord circuit for connecting said lines with said trunks, a plug for said cord circuit, talking strands in said coid circuit, said stra-nds being normally disconnected from said plug, a relay arranged to connect said strands to said plug, means for energizing said relay when said cord circuit connects a restricted line with a non-restricted trunk, or a non-restricted line With either a. restricted or non-restricted trunk, and means for preventing energization of said relay when said cord circuit connects a restricted line and a restricted trunk. Y y

20. In `a telephonek system, subscribers lines, trunk lines, means for interconnecting any of said lines with certain of said trunks, means for preventing the extension of calls from certain subscribers lines to certain.

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trunk lines, and means for preventing the extension of calls from certain trunk lines to certain subscribers lines.

2l. In a telephone system, a subscribers line, means for extending the line to a telephone switchboard over either of two paths, a cord circuit for use in extending connections from said line to other lines terminating at said switchboard and also from said line to trunks extending to a distant exvchanga'the talking strands of the cord being normally open, a relay cont-rolled oyer a connected one of said last mentioned llines but independent of control over a connected one of the trunks ior closing said talking circuit, additional means controlled over one I, only of said two paths for controlling said extending connection-s from said jacks to said manual substations and from certain oi" said jacks to a distant exchange, means for rendering .the cord circuit'inei'liective to extend a connection from the remaining jacks to the distant exchange, and means for rendering the first mentioned jacks inaccessible to the restricted substations.

23. In a telephone system, an operators position including a head set and a plurality of cord circuits, means including a key in each ot said cord circuits for connecting said cord circuit to said head set, means at said operators position for preventingmore than one ot' said cord circuits being connected to said head set at the same time, and a common key for disablingthe connecting means. I

24. In a telephone system, an operators position including a head setA and a plurality of Cord circuits, means including akey anda self-locking relayl'or connecting any one oit' said cord circuits to said head set and for preventing a plurality of said cord circuits being simultaneously connected to said head set, and a yflashing key having contacts in the self-locking circuit oi said relay.

In witness whereof, I hereunto subscribe my name this 19th day of March, A. 'D.. i925. l

'i THOMAS F. CROCKER. 

